1. Field of the Invention
The present invention relates to a differential gear that allows the difference of rotation between the left and right driving wheels of an automobile.
2. Description of the Prior Art
A differential gear is generally known as an apparatus that allows the difference of rotation between the left and right driving wheels of a vehicle when it travels curves in a road. The differential gear includes a pinion gear interposed between a pair of bevel gears coupled to the left and right axles of the driving wheels. If the shaft of the pinion gear is given an external rotational force, the pinion gear rotates on its axis during differential operation so that the difference of rotation between the axles is allowed. Such a differential gear has been utilized mainly in small tracks. In the differential gear for small tracks, the left and right axles of a vehicle are first inserted into the coupling holes provided in the bevel gears. Then, regulating members for antislip-out are mounted on the end portions of the left and right axles to regulate the movement of the axles in a direction (hereinafter referred to as a counter-insertion direction) opposite to the direction in which each axle is inserted. Furthermore, the end surfaces of the left and right axles abut the shaft of the pinion gear interposed between the bevel gears, thereby regulating the movement of each axle in the insertion direction in which the axle is inserted. A structure such as this renders it unnecessary to provide a complicated bearing for regulating the axial movement of each axle and has the advantage that the support structure for each axle can be constructed simply and inexpensively. For this reason, this structure has been utilized mainly in vehicles where low fabrication cost is desired, such as small trucks.
During travel on a road, if only one of the driving wheels runs on a road surface whose friction coefficient is extremely small, such as a snowy road surface and a sandy road surface, the one driving wheel will skid due to differential motion and the entire driving force will be lost, and in some cases, the vehicle cannot escape from that place. Also, while traveling curves in a road at high speeds, when the weight of the inner wheel is extremely reduced due to the centrifugal force, there arises the problem that the wheel skids on the road and therefore a driving force for traveling curves in the road at high speeds is lost. Hence, some vehicles are provided with a mechanism which limits the differential motion between the driving wheels in such a circumstance. It is general to employ a pressure clutch disc or a viscous coupling as a differential limiting mechanism. However, the differential limiting mechanism employing a clutch disc or a viscous coupling is a device which is added separately to the differential gear, so the structure becomes complicated and expensive, and even if the axle supporting structure were constructed at a low cost, there would arise the problem that the cost would be increased as a result of the complicated structure of the differential limiting mechanism.